Here's part of what the news release says:

"It seems unlikely that the same engine could produce both types of bursts, the team said. Although not directly addressed in the paper, these results support the notion that if the long bursts originate from massive stellar explosions, then short bursts originate from something entirely different. In the latter scenario, this event could be either mergers or such a drastic Jekyll-and-Hyde-like switch in the stellar explosion mode that the engine appears physically quite different. Such drastic and well-defined differences in the correlation between two of the major variables will need to be addressed quantitatively in future models of the burst physics. "

Which I think means that they still don't really know where they come from, but now they believe there are two ways for Gamma Ray Bursts to occur, whereas previously the puzzle only had one solution to seek.